CN109661535B

CN109661535B - Configurations and methods for small scale LNG production

Info

Publication number: CN109661535B
Application number: CN201680087367.9A
Authority: CN
Inventors: J.马克
Original assignee: Fluor Technologies Corp
Current assignee: Fluor Technologies Corp
Priority date: 2016-07-01
Filing date: 2016-07-05
Publication date: 2022-03-01
Anticipated expiration: 2036-07-05
Also published as: MX2023003745A; CN109661535A; US11112173B2; AU2016412662A1; BR112018077326A2; MX2018015551A; CA3027483C; US20210341221A1; CA3027483A1; US20180003429A1; WO2018004701A1

Abstract

An LNG plant includes a cold box and a refrigeration unit fluidly coupled with a plurality of heat exchanger passages in the cold box. The refrigeration unit is configured to provide a first refrigerant flow to a first heat exchanger pass of the plurality of heat exchanger passes at a first pressure, a second refrigerant flow to a second heat exchanger pass at a second pressure, and a third refrigerant flow to a third heat exchanger pass at a third pressure. The second refrigerant flow comprises a first portion of the first refrigerant flow, and the third refrigerant flow comprises a second portion of the first refrigerant flow. The second pressure and the third pressure are both lower than the first pressure. The cold box is configured to produce LNG from the natural gas feed stream to the cold box using refrigeration content from the refrigeration unit.

Description

Configurations and methods for small scale LNG production

Cross Reference to Related Applications

This application is PCT international application 35 u.s.c. § 119 and claims the benefit of U.S. patent application serial No. 15/201,070 entitled "construction and process for small LNG production" filed 2016, 7, 1, and entitled "co-pending" method and construction for small LNG production "according to 35 u.s.c. § 119, which is hereby incorporated by reference for all purposes as if reproduced in its entirety.

Statement regarding federally sponsored research or development

Not applicable.

Reference microfilm appendix

Not applicable.

Background

Natural gas supply in north america continues to increase, primarily due to the production of new shale gas (shal gas), recent discovery of offshore gas fields, and to a lesser extent, stranded natural gas that is put on the market after alaska natural gas pipeline construction, and it is believed that shale gas and coal bed methane (coal-bed methane) will account for the majority of future growth in the energy market.

While the supply of natural gas is increasing, the supply of crude oil is decreasing due to the lack of significant new discoveries of oil reserves. If this trend continues, transportation fuels derived from crude oil will soon become cost prohibitive and require replacement renewable fuels (and especially transportation fuels). Furthermore, the use of natural gas is even more desirable because combustion of natural gas also produces significantly less CO2 than other fossil materials (e.g., coal or gasoline). The natural gas used to transport the fuel must be in a more dense form, either as CNG (compressed natural gas) or LNG (liquefied natural gas). CNG is produced by compressing natural gas to very high pressures of about 3000 to 4000 psig. However, even at such pressures, the density of CNG is relatively low, and storage at high pressures requires heavy weight vessels and is potentially hazardous. In another aspect. LNG has a significantly higher density and can be stored at relatively low pressures of about 20 to 150 psig. Still further, LNG is a safer fuel than CNG because it is at a lower pressure and is not flammable until it vaporizes and mixes with air in the proper proportions. Nonetheless, CNG is more common than LNG as a transportation fuel, primarily due to high liquefaction costs and lack of infrastructure to support LNG refueling facilities.

LNG is available as a substitute for diesel fuel and is currently used in many heavy duty vehicles, including refuse trucks (refuse cranes), grocery delivery trucks (trucks), bus buses (transit buses), and coal mine lifts (coal mine lifts). To increase the LNG fuel market, small to medium LNG plants (LNG plants, sometimes also referred to as LNG plants or liquefied natural gas plants) must be built close to both the pipeline and the LNG consumers, because long distance transfer of LNG is expensive and therefore generally not economical. Such small to medium LNG plants should be designed to produce 0.2 to 2.0 mtpy (millions of tons per year). In addition, such small to medium LNG plants must be simple in design, easy to operate, and robust enough to support unmanned operation. Still further, it would be desirable to integrate liquefaction with LNG truck refueling operations to allow for even greater transportation flexibility.

Various refrigeration processes are used for LNG liquefaction. The most common of these refrigeration processes are cascade processes (cascade processes), mixed refrigeration processes, and propane pre-chilled mixed refrigerant processes. While these methods are energy efficient, such methods are often complex and require the circulation of several hydrocarbon refrigerants or mixed hydrocarbon refrigerants. Unfortunately, such refrigerants (e.g., propane, ethylene, and propylene) are explosive and dangerous in the event of a leak.

There are several recent innovations in LNG plant design. For example, U.S. patent No. 5,755,114 to Foglietta teaches a hybrid liquefaction cycle comprising a closed-loop propane refrigeration cycle and a turboexpander cycle. This liquefaction process has been simplified compared to other liquefaction processes, but is still unsuitable and/or economically unattractive for small to medium LNG plants. U.S. patent No. 7,673,476 to Whitesell discloses a compact and modular liquefaction system that does not require external refrigeration. The system uses gas expansion by recycling the feed gas to produce cooling. Although this design is relatively compact, the operation of the recirculation system is complex and the use of hydrocarbon gas for cooling remains a safety concern. U.S. Pat. No. 5,363,655 to Kikkawa teaches the use of a gas expander and a fin heat exchanger (fin heat exchanger) for LNG liquefaction. While providing several advantages, such a process is still too complex and expensive for small to medium LNG plants.

Further exacerbating the above-mentioned drawbacks, most systems in fact lack the ability to integrate small to medium LNG plants with LNG loading operations. Thus, current practices for loading LNG trucks typically require an LNG pump to pump LNG from the storage tank to the LNG truck. Notably, boil-off vapor (boil-off vapor) generated during LNG truck loading operations is vented to the atmosphere, which is a safety hazard and causes emission pollution.

Thus, various disadvantages still exist. Among them, most LNG liquefaction processes and configurations are complex and expensive, and thus are not suitable for small to medium LNG plants. Furthermore, most liquefaction plants lack an integrated system for LNG loading operations, which is highly desirable for small to medium LNG plants.

Disclosure of Invention

In one embodiment, the LNG plant includes a cold box comprising a plurality of heat exchanger passages and a refrigeration unit comprising a closed refrigeration cycle. The cold box is fluidly coupled to the refrigeration unit and is configured to receive the natural gas feed stream and produce LNG from the feed stream using refrigeration content (sometimes also referred to as content) from the refrigeration unit. The refrigeration unit includes a first compressor unit configured to compress a refrigerant to produce a compressed refrigerant at a first pressure; a first heat exchanger passage of the plurality of heat exchanger passages configured to pass the compressed refrigerant through the cold box to cool the compressed refrigerant; a separator configured to separate the cooled, compressed refrigerant into a first portion and a second portion; a first expander configured to receive the first portion from the separator and expand the first portion to a second pressure; a second expander configured to receive the second portion from the separator and expand the second portion to a third pressure; a second heat exchanger passage of the plurality of heat exchanger passages configured to pass the first portion through the cold box at a second pressure; a third heat exchanger pass of the plurality of heat exchanger passes configured to pass the second portion through the cold box at a third pressure to provide at least a portion of the refrigerated contents in the cold box; at least one second compressor configured to receive a second portion downstream of the third heat exchanger passage and compress the second portion to a second pressure; and a mixer configured to combine the compressed second portion downstream of the at least one second compressor with the first portion downstream of the second heat exchanger passage to form the refrigerant upstream of the first compressor. The second pressure is less than the first pressure, and the third pressure is less than the second pressure.

In one embodiment, the LNG plant includes a cold box including a heat exchanger having a plurality of heat exchanger passages and a refrigeration unit fluidly coupled to the plurality of heat exchanger passages. The refrigeration unit is configured to provide a first refrigerant flow to a first heat exchanger pass of the plurality of heat exchanger passes, a second refrigerant flow to a second heat exchanger pass of the plurality of heat exchanger passes, and a third refrigerant flow to a third heat exchanger pass of the plurality of heat exchanger passes at a first pressure. The second refrigerant flow includes a first portion of the first refrigerant flow downstream of the first heat exchanger pass, and the second refrigerant flow is at a second pressure. The third refrigerant flow includes a second portion of the first refrigerant flow downstream of the first heat exchanger pass, and the third refrigerant flow is at a third pressure. The second pressure and the third pressure are both lower than the first pressure. The cold box is configured to receive the natural gas feed stream and produce LNG from the natural gas feed stream using refrigeration content from the refrigeration unit in the plurality of heat exchanger passes.

In one embodiment, a method of producing LNG from a natural gas feed includes passing a first refrigerant stream through a first heat exchanger pass of a plurality of heat exchanger passes in a cold box at a first pressure, separating the first refrigerant stream into a second refrigerant stream and a third refrigerant stream downstream of the cold box, passing the second refrigerant stream through a second heat exchanger pass of the plurality of heat exchanger passes at a second pressure, passing the third refrigerant stream through a third heat exchanger pass of the plurality of heat exchanger passes, passing the natural gas feed stream through at least a fourth heat exchanger pass of the plurality of heat exchanger passes, and liquefying at least a portion of the natural gas stream in the cold box using refrigeration content provided by at least one of the second refrigerant stream or the third refrigerant stream to form an LNG stream. The third refrigerant flow is at a third pressure, and both the second pressure and the third pressure are lower than the first pressure.

Various objects, features, aspects and advantages will become more apparent from the following detailed description of various embodiments, along with the accompanying drawings.

Drawings

FIG. 1 is an exemplary configuration according to one embodiment using a nitrogen cycle.

FIG. 2 is another exemplary configuration according to one embodiment using a nitrogen cycle with integrated LNG loading.

Fig. 3 is an exemplary graph illustrating the approach temperature difference (temperature approach) of the thermal composition curve (heat composition curve) between the refrigeration loop and the feed gas of fig. 2.

Detailed Description

It should be understood at the outset that although illustrative embodiments of one or more embodiments are illustrated below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet existing. The present disclosure should in no way be limited to the illustrative embodiments, drawings, and techniques illustrated below, but may be modified within the full scope of the appended claims along with their full scope of equivalents.

The following brief definitions of terms shall apply throughout the application:

the term "comprising" means including but not limited to, and should be interpreted in the manner in which it is commonly used in the patent context;

the phrases "in one embodiment," "according to one embodiment," and the like generally mean that a particular feature, structure, or characteristic described after the phrase is included in at least one embodiment of the invention, and may be included in more than one embodiment of the invention (importantly, the phrases do not necessarily refer to the same embodiment);

if the specification describes certain terms as "exemplary" or "exemplary," it is understood to refer to a non-exclusive example;

the terms "about," "approximately," and the like, when used in conjunction with a number, may mean a specific number, or alternatively, a range near the specific number, as understood by those skilled in the art; and is

If the specification states that a component or part is "may", "should", "will", "preferably", "possible", "available", "typically", "optionally", "for example", "typically" or "may" (or other such language) contained or characterized, that particular component or part need not be contained or characterized. Such components and features may be optionally included or excluded in some embodiments.

The systems and methods described herein are directed to natural gas liquefaction and LNG (liquefied natural gas) truck loading, and in particular to the use of gas expansion processes for small to medium LNG plants and the integration of natural gas liquefaction with LNG truck loading facilities. As described herein, small to medium LNG plants may be integrated with LNG truck loading facilities in a simple and cost-effective manner. In some aspects, the small to medium LNG plant may have a capacity typically between about 0.2 mtpy and about 0.7 mtpy, typically between about 0.7 mtpy and about 1.5 mtpy, and most typically between about 1.5 mtpy and about 2.5 mtpy of LNG by liquefying an appropriate amount of feed gas. For some applications, contemplated processes may also be suitable for producing LNG below about 0.1 mtpy. In other aspects, the refrigeration process uses a non-hydrocarbon refrigerant (e.g., nitrogen, air, etc.) in the compression-expansion cycle to thus avoid the safety issues typically associated with hydrocarbon refrigeration systems.

As disclosed herein, natural gas (e.g., transported from a pipeline) may be liquefied in a cold box using a gas expansion cycle that employs a two-stage compressor to thus produce gas at least two pressure levels. The gas thus produced is then cooled and expanded to a lower pressure to produce refrigeration before being mixed into a single stream in a heat exchanger, which is then fed to a compressor driven by an expander.

The expander cycle may use nitrogen, which is inherently safe to operate and more reliable than conventional mixed refrigerant processes, while the nitrogen expander cycle may have a low or high pressure design to match the feed gas composition and pressure to the energy consumption of about 320 to about 425 kW/ton per unit of LNG produced.

In some embodiments, the LNG loading facility has a pressure control system that uses high pressure feed gas as power to move LNG product from the LNG storage tank to the LNG truck while recovering boil-off vapor from the LNG truck in the liquefaction plant.

In one aspect, a small to medium LNG plant may have an integrated loading terminal, wherein the plant comprises a cold box with a closed refrigeration cycle (preferably a two-stage expander refrigeration system operating with a non-hydrocarbon refrigerant) to thus provide refrigeration content to a natural gas feed at a temperature sufficient to produce LNG from the natural gas feed. It is generally preferred that the LNG storage tank is thermally coupled to a refrigeration cycle to receive and store LNG, and that the first boil-off vapor line provides a first boil-off vapor from the LNG carrier to the cold box and from the cold box to the LNG storage tank, while the second boil-off vapor line provides a second boil-off vapor from the LNG storage tank to the cold box and from the cold box to the natural gas feed. Most typically, a compressor compresses at least one of the first and second boil-off vapors, and/or a pressure differential controller maintains a predetermined pressure differential (e.g., 5-200 psi, more typically 10-50 psi) between the LNG storage tank and the LNG carrier.

In another aspect, LNG from the storage tank is offloaded from the top of the storage tank using internal pipes in the storage tank, which eliminates the potential risk of LNG spillage from the LNG tank inventory typically used in common tank configurations.

Thus, from a different perspective, a method of liquefying natural gas and loading LNG to an LNG carrier would include the steps of liquefying a natural gas feed in a cold box and supplying the LNG to an LNG storage tank using a closed refrigeration cycle. In another step, the first vaporized vapor from the LNG carrier is cooled and compressed and used as power to transfer LNG from the LNG storage tank to the LNG carrier. In such a process, the second vaporized vapor from the LNG storage tank may be cooled and compressed and moved from the cold box to the natural gas feed. As before, the step of liquefying the natural gas feed may be performed using a two-stage closed refrigeration cycle, typically using a non-hydrocarbon refrigerant, such as nitrogen.

Fig. 1 illustrates one embodiment of an LNG liquefaction system 100. The feed gas stream 102 may be supplied to a small LNG liquefaction plant. The feed gas stream may comprise primarily light hydrocarbons (light hydrocarbons), such as methane and ethane. Minor amounts of various other gases may also be present, including inert gases such as nitrogen, argon, and the like. The feed gas stream may be treated in a gas treatment unit, typically comprising an amine unit and a dehydration unit, for removal of CO2 and water, forming a dry and essentially CO 2-free gas stream. The feed gas stream may have a temperature between about 50 ° f and 200 ° f and a pressure between about 100 psia and 700 psia. Feed gas stream 102 may enter cold box 151, which may include a plurality of heat exchanger passages 152,153,154 and 155. Although four heat exchanger channels are shown in fig. 1, more than four heat exchanger channels or less than four heat exchanger channels may also be used with the system 100. The feed gas may be chilled by nitrogen refrigeration in heat exchanger channel 152 and formed into a sub-cooled LNG stream 103, which may then be reduced in pressure in a downstream JT valve to form a flashed LNG stream. The flash vapor may be returned to the liquefaction unit and the resulting liquid LNG may be stored in an LNG storage tank, as described in more detail herein.

The refrigeration for the cold box 151 may be provided by a closed refrigeration cycle. As shown in fig. 1, a closed refrigeration cycle may include a two-stage liquefaction cycle using a high pressure refrigerant cycle, typically operating at a pressure greater than about 1,000 psia. In the refrigeration cycle, stream 126 from compressor 150 may be discharged at a pressure between about 400 psia and 600 psia to supply compressor unit 160, which compresses the refrigerant gas to greater than about 1,000 psia (e.g., greater than 1,100 psia, greater than 1,200 psia, or greater than 1,300 psia) to form stream 128. Compressor unit 160 may typically have an upper compression limit of about 1,500 psia, although stream 126 may not be compressed to this limit in most configurations. Compressor unit 160 may comprise a single or multi-stage compressor, optionally with an intercooler. The compressor discharge may be cooled in cooler 164 to form stream 129, which may be further cooled in exchanger channel 155 to between-10F and about-50F in cold box 151, forming stream 130. Stream 130 can be divided into two parts: streams 130a and 130 b. The molar ratio (molar ratio) of the two streams can be divided into any suitable amounts, which can be based on the feed gas composition and/or pressure. In some aspects, the two streams 130a and 130b may be divided at a molar ratio of between about 0.5 and about 0.75, or between about 0.6 and about 0.7, or at about 0.68 of stream 130a to stream 130.

Stream 130a may be expanded in expander 170 to between about 20% and about 50%, or between about 30% and about 45%, or between about 35% and about 42% of the original pressure on an absolute pressure scale to form stream 179 through heat exchanger channel 153. Stream 179 can cool the feed gas stream 102 and the high pressure refrigerant stream 129 in the cold box 151. Stream 179 can flow from cold box 151 as stream 132. Stream 130b may be expanded in expander 180 on an absolute pressure scale to between about 3% and about 20%, or between about 4% and about 15%, or between about 5% and about 10%, or between about 7% and about 9% of the original pressure to form stream 127 through heat exchanger passage 154. Stream 127 may be used to cool the feed gas and high pressure refrigerant in cold box 151. Stream 127 can flow from cold box 151 as stream 121, which can then be compressed by compressor 150 to substantially the same pressure as stream 179, and stream 121 can then be mixed with stream 132 to form stream 120 as a feed to compressor 160.

In some cases, the use of two expanded refrigerant flow paths through the cold box 151 may allow for more efficient cooling. In one embodiment, the two lower pressure streams passing through the separate heat exchanger passages through the cold box 151 may have relative pressure ratios of between about 10:1 and about 2:1, between about 7:1 and about 3:1, or between about 5:1 and about 4:1, each on an absolute pressure scale as a ratio of the higher pressure refrigerant stream 179 to the lower pressure refrigerant stream 127.

Thus, a closed refrigeration cycle may include a cold box having a plurality of heat exchanger passages, including a plurality of heat exchanger passages for a refrigerant and at least one heat exchanger passage for a natural gas feed stream. A refrigeration unit is fluidly coupled to the cold box and the plurality of heat exchanger passages to provide a refrigerant and refrigeration content for forming LNG from the natural gas feed stream in the cold box. As shown in fig. 1, the refrigeration unit is configured to provide at least a first refrigerant flow to a first heat exchanger pass of the plurality of heat exchanger passes. The first flow of refrigerant may be at a first pressure, which may be a relatively high pressure after being compressed in the compressor unit 160. The refrigeration unit is also configured to provide a second flow of refrigerant to a second heat exchanger passage in the cold box. The second refrigerant flow may be a portion of the compressed refrigerant flow resulting from splitting the compressed refrigerant flow downstream of the first heat exchanger pass. The second refrigerant stream may be expanded (e.g., using an expander) such that the second refrigerant stream may be at a second pressure that is lower than the pressure of compression at the inlet to the second heat exchanger passage. The refrigeration unit may also provide a third refrigerant flow to the third heat exchanger pass. The third refrigerant flow may be the remainder of the compressed refrigerant flow resulting from splitting the compressed refrigerant flow downstream of the first heat exchanger pass. The third refrigerant stream may be expanded (e.g., using an expander) such that the third refrigerant stream is at a third pressure that is lower than the second pressure at the inlet to the third heat exchanger passage. The second and/or third heat exchanger passages may provide refrigeration content within the cold box. The resulting refrigeration content can then be used to form LNG from the natural gas in the natural gas feedstream, with an energy consumption of about 320 kW/ton to about 425 kW/ton per unit of LNG produced.

Fig. 2 illustrates another embodiment of an LNG production system 200. The refrigeration unit of fig. 2 is similar to the refrigeration unit of the system 100 illustrated in fig. 1, and the differences will be described in more detail with reference to fig. 2. In system 200, feed gas stream 201 may be supplied to an LNG liquefaction plant at any suitable flow rate (flowrate), temperature, and pressure. The feed gas stream may be the same as or similar to feed gas stream 102 described with respect to fig. 1, including composition, pressure, and temperature. In one embodiment and as one example of suitable conditions, feed gas stream 201 may be delivered at a flow rate of about 1.7 MMscfd at a temperature of about 100 ° f and at a pressure of about 453 psia. As a further example, the feed gas stream may have a composition that includes about 1.0 mol% N₂About 0.1 mol% CO₂About 96.5 mol% methane, about 2 mol% ethane, and about 0.5 mol% propane, and heavier components. The feed gas may be treated in a gas treatment unit 241, which may comprise an amine unit and/or a dehydration unit (e.g., a molecular sieve dehydration unit) for CO removal₂And water to form a substantially dry and CO-free mixture₂Of the gas stream 202.

As described in more detail herein, the dried gas stream 202 may be combined with the recirculated gas stream 211 and may enter a cold box 251, which generally includes a plurality of heat exchanger passages 152,153,154,155 and 156. Feed gas 102 may be chilled by nitrogen refrigeration in heat exchanger channel 152 to form subcooled stream 203, and then its pressure may be reduced in Joule-Thomson valve 271 to form stream 204. As one example, the subcooled stream may be cooled to about-223F and the flashed liquid downstream of the JT valve 271 may be at about-227F. The flashed liquid may be stored in a storage tank 265, which may operate at a pressure above atmospheric, such as between about 20 psia and 100 psi, or at about 60 psia. Flash gas stream 208 can be recovered by recycling the gas in stream 208 back to exchanger channel 156 via valve 270. When the gas in stream 208 is in equilibrium with the liquid in reservoir 265, the gas may have a temperature that is lower than the temperature of the other streams in cold box 151. The refrigeration content of this recycle stream may be recovered in cold box 151. Thus, it should be noted that the flash stream from storage tank 265 may be heated in cold box 151. Once the gas stream passes through cold box 151 to form stream 210, stream 210 can exit cold box 151 and be compressed by compressor 268 to a pressure at or above the feed gas pressure to form stream 211 before being mixed with feed gas stream 102.

As described above with respect to fig. 1, the two-stage nitrogen liquefaction cycle may also be configured using a high pressure nitrogen cycle, typically operating above 1,000 psia (e.g., at or above about 1,100 psia, 1,200 psia, 1,300 psia, etc.). As long as the gas is dry, nitrogen or air can be used in the cycle. The hydrocarbon content is monitored to detect any leaks as is known in the art, and the unit may be immediately shut down during an emergency. The refrigeration cycle shown in fig. 2 is similar to the refrigeration cycle shown in fig. 1, except that the compressor unit 160 shown in fig. 1 may include a two-stage compressor as shown in fig. 2. Further, the compressor unit 150 that compresses a portion of the refrigerant flow may include two-stage compression, where the two-stage compression may be mechanically coupled to parallel expanders 170,180, as shown in fig. 1.

Gas pretreatment, steam handling (vapor handling) and loading systems are the same as previous designs; the difference lies in the design of the liquefaction cycle. As shown in fig. 1, the feed gas is chilled and at least partially liquefied in exchanger channel 152 by a refrigeration cycle to form a subcooled stream 103. As one example, the subcooled stream may be at about-238F and then its pressure may be reduced in JT valve 271 as described above to form stream 204 that is passed to storage tank 265.

Within the refrigeration cycle, stream 226 from compressor 260, which may optionally be mechanically coupled to expander 259, may be discharged and optionally cooled in ambient cooler 212 before being combined with stream 132 to form a feed to the compressor unit. As one example, stream 226 may be compressed to about 507 psia prior to being combined with stream 132. The compressor unit may comprise a two-stage refrigerant compressor unit including a compressor 261 and a compressor 262 along with an intercooler 263. For example, stream 120 may be compressed in compressor 261, compressed stream 22 may be passed to intercooler 263, and then cooled, compressed stream 223 may be passed to second stage compressor 262. The compressor unit may compress the refrigerant to a high pressure above 1,000 psi or another of the other pressures disclosed herein. Compressed refrigerant stream 128 can be cooled in ambient cooler 164 to form stream 129. The ambient cooler 164 may include any suitable heat exchanger to cool the compressed refrigerant, such as an air exchanger, a water exchanger, and the like.

Stream 129 may pass from ambient cooler 164 to cold box 151 and through heat exchanger passage 155 to cool the high pressure refrigerant stream and form stream 130. As one example, the refrigerant in stream 129 may be cooled to form stream 130 at about-30F. Stream 130 may then be split into two portions, including streams 130a and 130 b. The molar ratio of the two streams may be divided into any suitable amounts (e.g., as disclosed with respect to fig. 1), which may be based on the feed gas composition and/or pressure. In some aspects, the two streams 130a and 130b can be separated in any molar ratio described with respect to fig. 1.

Stream 130a can be expanded in expander 257 to form stream 179. The expander 257 may be the same as or similar to the expander 170 described with respect to fig. 1. The expander may expand stream 130a according to any of the pressure ranges described with respect to fig. 1. As one example, stream 130a may be expanded from about 1282 psia to about 508 psia, which is a proportion of about 40%. Expansion of stream 130a in expander 257 can result in the formation of stream 179, which can be passed back to cold box 151 in heat exchanger channel 153. As one example, the expansion of stream 130a may result in stream 179 having a temperature of about-126 ° F. Stream 179 can be used to cool feed gas stream 102 and high pressure nitrogen stream 129 in heat exchanger channel 153 to form stream 132. As one example, stream 132 may exit cold box 151 at about 507 psia and about 94 ° F.

Stream 130b can be expanded in expander 259 to form stream 127. The expander 159 may be the same as or similar to the expander 180 described with respect to fig. 1. Expander 159 may expand stream 130b according to any of the pressure ranges described with respect to fig. 1. Further, the relative pressure ratio of the two expanded streams to each other and to the high pressure stream may fall within any of the ranges described with respect to fig. 1. As one example, stream 130b may be expanded from about 1282 psia to about 110 psia using expander 259, which results in stream 127 having a pressure of about 8.5% of the pressure of stream 130 b. The expansion may result in stream 127 having a lower temperature, e.g., about-242F. Stream 127 can then be used to cool feed gas 102 and the high pressure refrigerant stream in heat exchanger passage 154. The low pressure stream 121 may then be compressed prior to being combined with stream 132. As shown in fig. 2, stream 121 can be compressed by compressor 258, through line 233, and compressed by second stage compressor 260 to compress a portion of the refrigerant to a pressure at or above the pressure in stream 132. In contrast to FIG. 1, the compression of stream 121 may be performed in two stages of compression using compressors 258,260 arranged in series. As one example of compression conditions, stream 121 may be compressed in compressors 258,260 to about 508 psia, such that stream 121 may be combined with stream 132 to form stream 120 as a feed to

refrigerant compressors

261, 262.

The expansion and compression cycles may be mechanically coupled as shown in fig. 2. For example, the expanders used to expand streams 130a and 130b may be mechanically coupled to the compressor for the low pressure stream 121 exiting the heat exchanger passage 154. Specifically, expander 257 may be mechanically coupled to compressor 258, and compressor 259 may be mechanically coupled to compressor 260. This type of configuration may be used to reduce the overall compression energy requirement. Fig. 3 illustrates a thermal recombination curve showing the temperature difference between the feed gas and the refrigeration loop according to the system described with respect to fig. 2. The composite thermal profile indicates efficiency in the natural gas liquefaction implementing the system described herein.

During conventional LNG truck loading operations, LNG is typically pumped from a storage tank to an LNG truck using an LNG pump. This operation takes at least 2 hours because the LNG truck must be chilled from normal ambient temperature to cryogenic temperatures. This operation also produces significant quantities of vaporized vapor which is in most cases vented to the atmosphere and therefore presents a significant environmental concern.

Instead, and as shown in fig. 2, LNG may be transferred from the LNG storage tank 265 to the LNG carrier 267 via streams 205,206 and loading hose 266 by a pressure differential, thereby allowing a filling operation to be performed without the use of an LNG pump. LNG may be diverted from top outlet nozzle 298 using an internal pipe 299 within storage tank 265. This configuration helps to avoid any bottom nozzles from the tank 265, thereby avoiding spillage of tank inventory commonly encountered in conventional tank designs. Thus, no LNG pump is required. A flow controller 282 may be adjusted as necessary to deliver a flow quantity to the LNG carrier 267. When the level (level) in the storage tank 265 falls to a low level, the level control 297 may reduce or stop the flow in the stream 205 at a predetermined low level. The LNG storage tank 265 may be configured with a capacity of between about 10,000 gallons and about 50,000 gallons or about 30,000 gallons, which is sufficient to load at least two LNG carriers 267, such as LNG trucks with 10,000 gallons of capacity each. During LNG truck loading operations, valve 270 is closed and valve 269 is opened, allowing vaporized vapor stream 207 to vent from LNG carrier 267 as stream 209 to cold box 151. The valve 269 may control the LNG transport vapor header (header) at about 50 psig, a lower pressure set point for the LNG carrier 267, using the pressure controller 281. Wherein these valves are operated in series to recover the boil-off vapor during loading and avoid venting to the atmosphere. In some embodiments, the vaporized vapor may be at a lower temperature than the flow in the cold box 151, and directing these vaporized vapors back to the cold box 151 may allow the refrigerant content of the vaporized vapor to be recovered in the cold box 151.

To provide the driving force to pressurize the LNG inventory within storage tank 265 and transfer LNG from storage tank 265 to LNG carrier 267, valve 284 may be opened to provide the high pressure gas in stream 285 to storage tank 265. Pressure differential controller 288 and pressure controller 283 may be used to control the flow rate of LNG to LNG carrier 267. Typically, the pressure differential may be set at about 10 psi or higher depending on the distance between the storage tank 265 and the LNG carrier 267. The LNG loading rate may vary from about 250 GPM to about 500 GPM using flow controller 282. Generally, the pressure differential can be increased to increase the loading rate. Thus, it should be appreciated that LNG pumping is not necessary and that loading system size and cost can be significantly reduced.

While the contemplated methods and apparatus presented herein may have any capacity, it should be recognized that such apparatus and methods are particularly suitable for small to medium LNG plants that have a capacity of typically between 0.2 to 0.7 mtpy (million tons per year) of LNG production, more typically between 0.7 to 1.5 mtpy, and most typically between 1.5 to 2.5 mtpy, by liquefaction of an appropriate amount of feed gas. Thus, contemplated plants and methods may be practiced at any location where large quantities of natural gas are available, and particularly preferred locations include gas producing wells (gas producing wells), gasification plants (e.g., coal and other carbonaceous materials), and decentralized locations using gas from natural gas pipelines. Thus, it should be recognized that the feed gas composition may vary significantly and that one or more pretreatment units may be required depending on the type of gas composition. For example, suitable pretreatment units include dehydration units, acid gas removal units, and the like.

It is also noted that the use of a cold box with inert gas is particularly preferred, especially in the case of liquefaction/filling stations in urban environments. However, various other cryogenic devices are also considered suitable, and alternative devices include those that use mixed hydrocarbon refrigerants. Furthermore, especially in case of tanks with somewhat larger capacity, it is expected that the refrigeration content from LNG may also be used to supplement the refrigeration requirements.

With respect to the differential pressure controller (dPC), it is noted that dPC is preferably implemented as a control device having a CPU, and thus may be configured as a suitably programmed personal computer or programmable logic controller. It is also generally preferred that dPC be configured such that dPC controls the operation of control valves to maintain a predetermined pressure differential between the storage tank and the tanks in the LNG transport vessel using pressure sensors and valves, as is well known in the art. For example, control may be achieved by adjusting the pressure and/or flow volume (also sometimes referred to as flow) of the compressed boil-off vapor en route from the compressor outlet to the storage tank, by adjusting the pressure and/or flow volume of the boil-off vapor from the tank in the LNG transport vessel, and/or by adjusting the pressure and/or flow volume of the LNG from the storage tank to the tank in the LNG transport vessel. Thus, in at least some embodiments, the pressure differential controller will be configured to allow liquefaction operations to be concurrent with the filling operations of the LNG carrier. Thus, the feeding of natural gas to the liquefaction unit is done in a continuous manner. However, discontinuous feeding and liquefaction are also contemplated.

It should be noted that, in contrast to most known configurations, at least a portion of the boil-off vapor from the storage tank and/or the tank in the LNG transport vessel is not liquefied, but is used as a motive fluid to move LNG from the storage tank to the tank in the LNG transport vessel. Thus, the need for an LNG pump is eliminated. Further, it should be noted that the refrigeration content of the boil-off vapor from the tanks in the LNG transport vessel may be used for supplemental refrigeration requirements in the cold box. Thus, as is known in most operations, the vaporized vapor is heated rather than cooled and reliquefied.

It is still further contemplated that the storage tank may be modified in such a manner that LNG carried out of the storage tank is drawn out of a lower portion of the storage tank (e.g., a sump (sometimes also referred to as a sump) or other location, typically below the center of gravity of the tank) through the vapor space of the tank to a fill line/hose, thereby avoiding problems associated with a fill port at the lower portion of the storage tank. Most often, the tank will contain an internal filling pipe which terminates at a higher part of the tank, to thus allow connection of the internal filling pipe to a filling line/filling hose.

Having described the systems and methods herein, various aspects may include, but are not limited to:

in a first aspect, an LNG plant includes a cold box comprising a plurality of heat exchanger channels; and a refrigeration unit comprising a closed refrigeration cycle, wherein the cold box is fluidly coupled to the refrigeration unit, wherein the cold box is configured to receive the natural gas feed stream and produce LNG from the feed stream using refrigeration content from the refrigeration unit, wherein the refrigeration unit comprises: a first compressor unit configured to compress a refrigerant to produce a compressed refrigerant at a first pressure; a first heat exchanger pass of the plurality of heat exchanger passes, wherein the first heat exchanger pass is configured to pass compressed refrigerant through a cold box to cool the compressed refrigerant; a separator configured to separate the cooled, compressed refrigerant into a first portion and a second portion; a first expander configured to receive the first portion from the separator and expand the first portion to a second pressure, wherein the second pressure is less than the first pressure; a second expander configured to receive the second portion from the separator and expand the second portion to a third pressure, wherein the third pressure is less than the second pressure; a second heat exchanger passage of the plurality of heat exchanger passages configured to pass the first portion through the cold box at a second pressure; a third heat exchanger pass of the plurality of heat exchanger passes configured to pass the second portion through the cold box at a third pressure to provide at least a portion of the refrigerated contents in the cold box; at least one second compressor, wherein the at least one second compressor is configured to receive a second portion downstream of the third heat exchanger passage and compress the second portion to a second pressure; and a mixer, wherein the mixer is configured to combine the compressed second portion downstream of the at least one second compressor with the first portion downstream of the second heat exchanger passage to form the refrigerant upstream of the first compressor.

A second aspect may include the LNG plant of the first aspect, wherein the first compressor unit comprises a plurality of compressors arranged in series and an intercooler disposed between successive compressors.

A third aspect may include the LNG plant of the first or second aspect, wherein the at least one second compressor comprises a plurality of second compressors, and wherein at least one of the plurality of second compressors is mechanically coupled to the first expander or the second expander.

A fourth aspect may include the LNG plant of any of the first to third aspects, wherein the second pressure is between about 20% and about 50% of the first pressure on an absolute scale (also sometimes referred to as an absolute temperature scale).

A fifth aspect may include the LNG plant of any of the first to fourth aspects, wherein the third pressure is between about 3% and about 20% of the first pressure on an absolute scale.

A sixth aspect may include the LNG plant of any one of the first to fifth aspects, further comprising a heat exchanger fluidly coupled between the first compressor and the first heat exchanger channel, wherein the heat exchanger is configured to cool the compressed refrigerant before passing to the first heat exchanger channel.

In a seventh aspect, an LNG plant comprises a cold box comprising a heat exchanger, wherein the heat exchanger comprises a plurality of heat exchanger channels; a refrigeration unit fluidly coupled with the plurality of heat exchanger channels, wherein the refrigeration unit is configured to: providing a first refrigerant flow to a first heat exchanger pass of the plurality of heat exchanger passes, wherein the first refrigerant flow is at a first pressure; providing a second refrigerant stream to a second heat exchanger pass of the plurality of heat exchanger passes, wherein the second refrigerant stream comprises a first portion of the first refrigerant stream downstream of the first heat exchanger pass, and wherein the second refrigerant stream is at a second pressure; and providing a third refrigerant flow to a third heat exchanger pass of the plurality of heat exchanger passes, wherein the third refrigerant flow comprises a second portion of the first refrigerant flow downstream of the first heat exchanger pass, and wherein the third refrigerant flow is at a third pressure, wherein the second pressure and the third pressure are both lower than the first pressure; wherein the cold box is configured to receive a natural gas feed stream and produce LNG from the natural gas feed stream using refrigeration content from the refrigeration unit in the plurality of heat exchanger passes.

An eighth aspect may include the LNG plant of the seventh aspect, wherein the first pressure is between about 1,000 psia and 2,000 psia.

A ninth aspect may include the LNG plant of the seventh or eighth aspect, wherein the second pressure is between about 20% and about 50% of the first pressure on an absolute scale.

A tenth aspect may include the LNG plant of any of the seventh to ninth aspects, wherein the third pressure is between about 3% and about 20% of the first pressure on an absolute scale.

The eleventh aspect may include the LNG plant of any of the seventh to tenth aspects, wherein the ratio of the second pressure to the third pressure is between about 10:1 and about 2: 1.

A twelfth aspect may include the LNG plant of any of the seventh to eleventh aspects, wherein the molar ratio of the flow rate of the second refrigerant stream to the flow rate of the first refrigerant stream is between about 0.5 and about 0.75.

A thirteenth aspect may include the LNG plant of any of the seventh to twelfth aspects, wherein the refrigeration unit is configured to provide LNG at an energy between about 320 kW/ton and about 425 kW/ton.

In a fourteenth aspect, a method of producing LNG from a natural gas feed includes passing a first refrigerant stream through a first heat exchanger pass of a plurality of heat exchanger passes in a cold box, wherein the first refrigerant stream is at a first pressure; separating the first refrigerant stream into a second refrigerant stream and a third refrigerant stream downstream of the cold box; passing a second refrigerant stream through a second heat exchanger pass of the plurality of heat exchanger passes, wherein the second refrigerant stream is at a second pressure; passing a third refrigerant flow through a third heat exchanger pass of the plurality of heat exchanger passes, wherein the third refrigerant flow is at a third pressure, wherein the second pressure and the third pressure are both lower than the first pressure; passing the natural gas feedstream through at least a fourth heat exchanger pass of the plurality of heat exchanger passes; and liquefying at least a portion of the natural gas stream in the cold box using refrigeration content provided by at least one of the second refrigerant stream or the third refrigerant stream to form an LNG stream.

A fifteenth aspect may include the method of the fourteenth aspect, further comprising combining the second refrigerant flow with the third refrigerant flow downstream of the cold box to form a recycle flow; and compressing the recycle stream to form a first refrigerant stream.

A sixteenth aspect can include the method of the fifteenth aspect, wherein compressing the recycle stream includes compressing the recycle stream in a two-stage compressor.

A seventeenth aspect may include the method of the fifteenth or sixteenth aspect, further comprising expanding the second refrigerant stream to a second pressure in a first expander; expanding the third refrigerant stream in a second expander to a third pressure, wherein the second pressure is between about 20% and about 50% of the first pressure on an absolute scale; and compressing the third refrigerant stream prior to combining the second refrigerant stream with the third refrigerant stream.

An eighteenth aspect may include the method of the seventeenth aspect, wherein at least one of the first expander or the second expander is coupled to a compressor, wherein compressing the third refrigerant stream prior to combining the second refrigerant stream with the third refrigerant stream comprises compressing the third refrigerant stream using the compressor.

The nineteenth aspect may include the method of any one of the fourteenth to eighteenth aspects, wherein the second pressure is between about 20% and about 50% of the first pressure on an absolute scale.

A twentieth aspect may include the method of any one of the fourteenth to nineteenth aspects, wherein the third pressure is between about 3% and about 20% of the first pressure on an absolute scale.

Thus, specific embodiments and applications of small LNG production and filling have been disclosed. It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the concepts herein described. The subject matter, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. In the case where the specification or claims refer to at least one selected from the group consisting of a, B, C … and N, then the text should be interpreted as requiring only one element from the group, rather than a plus N, or B plus N, etc.

Claims

1. An LNG plant, comprising:

a cold box comprising a plurality of heat exchanger channels;

a gas treatment unit comprising an amine unit and a dehydration unit; and

a refrigeration unit comprising a closed refrigeration cycle, wherein the cold box is fluidly coupled to the refrigeration unit, wherein the cold box is configured to receive a natural gas feed stream and produce LNG from the natural gas feed stream using refrigeration content from the refrigeration unit, wherein the refrigeration unit comprises:

a multi-stage compressor configured to compress a first refrigerant stream to produce a compressed first refrigerant stream at a first pressure;

a first heat exchanger pass of the plurality of heat exchanger passes, wherein the first heat exchanger pass is configured to pass the compressed first refrigerant stream through the cold box to cool the compressed first refrigerant stream;

a separator configured to separate the cooled and compressed first refrigerant stream into a first portion and a second portion;

a first expander configured to receive the first portion from the separator and expand the first portion to a second pressure, wherein the second pressure is less than the first pressure;

a second expander configured to receive the second portion from the separator and expand the second portion to a third pressure, wherein the third pressure is less than the second pressure;

a second heat exchanger passage of the plurality of heat exchanger passages configured to pass the first portion through the cold box at the second pressure;

a third heat exchanger pass of the plurality of heat exchanger passes configured to pass the second portion through the cold box at the third pressure to provide at least a portion of the refrigerated contents in the cold box;

a first compressor followed by a second compressor, wherein the first compressor is configured to receive the second portion downstream of the third heat exchanger passage and compress the second portion to the second pressure by the first compressor and the second compressor, wherein the first compressor is coupled to the first expander and the second compressor is coupled to the second expander; and

a mixer upstream of the multi-stage compressor and downstream of the second compressor, wherein the mixer is configured to combine the compressed second portion downstream of the second compressor with the first portion downstream of the second heat exchanger passage to form the first refrigerant flow upstream of the multi-stage compressor.

2. The LNG plant of claim 1, wherein the multi-stage compressor comprises a plurality of compressors arranged in series and an intercooler disposed between successive compressors.

3. The LNG plant of claim 1, wherein the first compressor is coupled to the first expander and the second compressor is coupled to the second expander.

4. The LNG plant of claim 1, wherein the second pressure is between 20% and 50% of the first pressure on an absolute scale.

5. The LNG plant of claim 1, wherein the third pressure is between 3% and 20% of the first pressure on an absolute scale.

6. The LNG plant of claim 1, further comprising a heat exchanger fluidly coupled between the multi-stage compressor and the first heat exchanger passage, wherein the heat exchanger is configured to cool the compressed first refrigerant stream prior to the compressed first refrigerant stream passing to the first heat exchanger passage.

7. An LNG plant comprising:

a cold box comprising a heat exchanger, wherein the heat exchanger comprises a plurality of heat exchanger channels;

a refrigeration unit fluidly coupled with the plurality of heat exchanger channels, wherein the refrigeration unit is configured to:

providing a first refrigerant flow to a first heat exchanger pass of the plurality of heat exchanger passes, wherein the first refrigerant flow is at a first pressure;

providing a second refrigerant stream to a second heat exchanger pass of the plurality of heat exchanger passes, wherein the second refrigerant stream is a first portion of the first refrigerant stream downstream of the first heat exchanger pass, and wherein the second refrigerant stream is at a second pressure; and is

Providing a third refrigerant flow to a third heat exchanger pass of the plurality of heat exchanger passes, wherein the third refrigerant flow is a second portion of the first refrigerant flow downstream of the first heat exchanger pass, and wherein the third refrigerant flow is at a third pressure, wherein the second pressure and the third pressure are both lower than the first pressure;

wherein the refrigeration unit comprises:

a separator configured to separate the first refrigerant stream into the second refrigerant stream and the third refrigerant stream;

a first expander configured to receive the second refrigerant stream from the separator and expand the second refrigerant stream to the second pressure, wherein the second pressure is less than the first pressure;

a second expander configured to receive the third refrigerant stream from the separator and expand the third refrigerant stream to the third pressure, wherein the third pressure is less than the second pressure;

a first compressor followed by a second compressor, the first compressor configured to receive the third refrigerant stream from the third heat exchanger passage and compress the third refrigerant stream through the first compressor and the second compressor to a fourth pressure equal to or higher than the second pressure, wherein the first compressor is coupled to the first expander and the second compressor is coupled to the second expander; and

a two-stage compressor configured to compress a recycle stream to form the first refrigerant stream, wherein the third refrigerant stream and the second refrigerant stream are combined downstream of the second compressor and upstream of the two-stage compressor and the first heat exchanger pass to form the recycle stream,

wherein the cold box is configured to receive a natural gas feed stream and produce LNG from the natural gas feed stream using refrigeration content from the refrigeration unit in the plurality of heat exchanger passages.

8. The LNG plant of claim 7, wherein the first pressure is between 1,000 psia and 2,000 psia.

9. An LNG plant according to claim 7, wherein the second pressure is between 20% and 50% of the first pressure on an absolute scale.

10. An LNG plant according to claim 7, wherein the third pressure is between 3% and 20% of the first pressure on an absolute scale.

11. The LNG plant of claim 7, wherein a ratio of the second pressure to the third pressure is between 10:1 and 2: 1.

12. An LNG plant according to claim 7, wherein the molar ratio of the flow rate of the second refrigerant stream to the flow rate of the first refrigerant stream is between 0.5 and 0.75.

13. The LNG plant of claim 7, wherein the refrigeration unit is configured to provide the LNG at between 320 kW/ton and 425 kW/ton of energy.

14. A method of producing LNG from a natural gas feed, comprising:

passing a first refrigerant stream through a first heat exchanger pass of a plurality of heat exchanger passes in a cold box, wherein the first refrigerant stream is at a first pressure;

separating the first refrigerant stream into a second refrigerant stream and a third refrigerant stream downstream of the cold box by passing the first refrigerant stream through a separator;

said second refrigerant stream is expanded in a first expander to a second pressure;

after expanding the second refrigerant stream, passing the second refrigerant stream through a second heat exchanger pass of the plurality of heat exchanger passes at the second pressure;

said third refrigerant stream is expanded in a second expander to a third pressure;

after expanding the third refrigerant stream, passing the third refrigerant stream through a third heat exchanger pass of the plurality of heat exchanger passes at the third pressure, wherein the second pressure and the third pressure are both lower than the first pressure;

compressing the third refrigerant stream to a fourth pressure equal to or higher than the second pressure by a first compressor and then by a second compressor after passing the third refrigerant stream through the third heat exchanger pass, wherein the first compressor is coupled to the first expander and the second compressor is coupled to the second expander;

cooling the third refrigerant stream after compressing the third refrigerant stream;

after cooling the third refrigerant stream, combining the second refrigerant stream and the third refrigerant stream downstream of the cold box to form a recycle stream;

compressing the recycle stream in a two-stage compressor to form the first refrigerant stream;

passing a natural gas feedstream through at least a fourth heat exchanger pass of the plurality of heat exchanger passes; and is

Liquefying at least a portion of the natural gas feed stream in the cold box using refrigeration content provided by at least one of the second refrigerant stream or the third refrigerant stream to form an LNG stream,

wherein the first expander is disposed downstream of the separator.

15. The method of claim 14, wherein the second pressure is between 20% and 50% of the first pressure on an absolute scale.

16. The method of claim 14, wherein the first expander is coupled to the first compressor, wherein the second expander is coupled to the second compressor.

17. The method of claim 14, wherein the third pressure is between 3% and 20% of the first pressure on an absolute scale.